Voltage ripple detection and driver control for stable output current

ABSTRACT

According to some embodiments, there is provided a power supply system including a converter configured to generate an output signal based on a rectified input signal for driving a light source, an output correction circuit coupled to an output of the converter and configured to measure a ripple in the output signal and to generate a correction signal to dynamically control a DC-level of the output signal of the converter based on the measured ripple and a reference signal corresponding to a desired DC-level of the output signal.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to and the benefit of U.S. ProvisionalPatent Application No. 63/082,835, filed in the United States Patent andTrademark Office on Sep. 24, 2020, the entire disclosure of which isincorporated by reference herein.

FIELD

Aspects of the present invention are related to power supply systems forlight sources.

BACKGROUND

A light emitting diode (LED) is an electronic device that convertselectrical energy (commonly in the form of electrical current) intolight. The light intensity of an LED is primarily based on the magnitudeof the driving current. Given that an LED luminosity is very sensitiveto drive current changes, in order to obtain a stable luminous outputwithout flicker, it is desirable to drive LEDs by a constant-currentsource.

Generally, lighting sources are powered by an input AC voltage of 110 or220 VAC at 50 or 60 Hz line frequency. The input AC voltage is rectifiedvia a rectifier and converted to a desired output voltage level thatwill be utilized by the LED. As any input power ripple may induce anoutput voltage ripple and output current ripple, a feedback loop thatmeasures the output of the converter may be used to implement ripplecontrol and to adjust the output signal. However, the output ripple mayaffect the feedback loop in a way that causes the output signal to be ata DC value that does not reflect the desired value.

The above information disclosed in this Background section is only forenhancement of understanding of the invention, and therefore it maycontain information that does not form the prior art that is alreadyknown to a person of ordinary skill in the art.

SUMMARY

Aspects of embodiments of the present invention are directed to a powersupply system utilizing a secondary-side output correction circuit thatgenerates a feedback control signal, which allows the DC-DC converter toaccurately set the DC level of the output signal despite the presence ofoutput ripple. In some embodiments, the output correction circuit iscapable of adjusting the feedback control signal based on observedripple at the output.

According to some embodiments, there is provided a power supply systemincluding: a converter configured to generate an output signal based ona rectified input signal for driving a light source; an outputcorrection circuit coupled to an output of the converter and configuredto measure a ripple in the output signal and to generate a correctionsignal to dynamically control a DC-level of the output signal of theconverter based on the measured ripple and a reference signalcorresponding to a desired DC-level of the output signal.

In some embodiments, the output signal is an output current or an outputvoltage of the converter, and the converter is a DC-DC converter.

In some embodiments, wherein the output correction circuit includes: asense resistor electrically coupled between an output terminal of theconverter and the light source driven by the converter; and a currentsense circuit coupled to the sense resistor and configured to measure anoutput current of the converter via the sense resistor, and to generatea sense signal corresponding to the measured output current.

In some embodiments, the output correction circuit includes: a senseresistor configured to sense an output current of the converter; areference generator configured to generate an adjusted reference signal;and an operational amplifier configured to receive the adjustedreference signal and a sense signal corresponding to the sensed outputcurrent, and to generate the correction signal based on a differencebetween the adjusted reference signal and the sensed output current.

In some embodiments, the reference generator is configured to monitor anoutput voltage of the converter, to determine a percentage ripple in theoutput signal based on the monitored output voltage, and to adjust thereference signal based on the percentage ripple.

In some embodiments, the reference generator is further configured tomeasure a peak-to-peak voltage ripple in the output voltage and aDC-level of the output voltage, and to calculate the percentage ripplebased on the peak-to-peak voltage ripple and the DC-level of the outputvoltage.

In some embodiments, the reference generator is further configured tocalculate a correction factor based on the calculated percentage rippleand a look-up table (LUT) including ordered pairs of percentage ripplesand associated correction factors.

In some embodiments, the reference generator is further configured tocalculate the correction factor by interpolating between two adjacentcorrection factors stored in the LUT.

In some embodiments, the reference generator is further configured tocalculate the adjusted reference signal by multiplying the referencesignal by the correction factor.

In some embodiments, the reference generator is further configured tocalculate a correction factor based on the calculated percentage rippleand a formula that relates correction factors to percentage ripples.

In some embodiments, the reference generator includes: a memoryconfigured to store a look-up table (LUT) including ordered pairs ofpercentage ripples and associated correction factors; and a processorconfigured to calculate a correction factor based on and the LUTincluding ordered pairs of percentage ripples and associated correctionfactors, and to calculate the adjusted reference signal based on thereference signal and the correction factor.

In some embodiments, the memory is configured to store a plurality ofLUTs corresponding to different values of an output capacitance of thepower supply system.

In some embodiments, the reference generator is configured to receivethe reference signal from a dimming controller, the reference signalbeing based on a dimmer setting.

In some embodiments, the output correction circuit is electricallyisolated from a primary side of the converter.

In some embodiments, the power supply system further includes: arectifier configured to rectify an input signal to generate therectified input signal having a single polarity.

In some embodiments, the output correction circuit is configured toprovide the correction signal to the converter, and the converter isconfigured to regulate a DC-level voltage of the output signal based onthe correction signal.

In some embodiments, the power supply system further includes: a powerfactor correction (PFC) controller coupled to a primary side of theconverter, wherein the output correction circuit is configured toprovide the correction signal to the PFC controller, and wherein the PFCcontroller is configured to regulate a DC-level voltage of the outputsignal based on the correction signal.

In some embodiments, the converter has a primary side and a secondaryside electrically isolated from, and inductively coupled to, the primaryside.

In some embodiments, the output correction circuit is configured tocommunicate the correction signal to a primary side of the converter viaan optocoupler.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, together with the specification, illustrateexample embodiments of the present invention, and, together with thedescription, serve to explain the principles of the present invention.

FIG. 1 illustrates a lighting system including a power supply systemhaving an output correction circuit, according to some exampleembodiments of the present disclosure.

FIG. 2 is a schematic diagram illustrating the output correction circuitwithin the power supply system, according to some example embodiments ofthe present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below is intended as a description ofexample embodiments of power supply system (e.g., an LED driver) with anoutput correction circuit and driver control system, provided inaccordance with the present invention and is not intended to representthe only forms in which the present invention may be constructed orutilized. The description sets forth the features of the presentinvention in connection with the illustrated embodiments. It is to beunderstood, however, that the same or equivalent functions andstructures may be accomplished by different embodiments that are alsointended to be encompassed within the spirit and scope of the invention.As denoted elsewhere herein, like element numbers are intended toindicate like elements or features.

FIG. 1 illustrates a lighting system 1 including a power supply system30 having an output correction circuit 100, according to some exampleembodiments of the present disclosure.

According to some embodiments, the lighting system 1 includes an inputsource 10, a light source 20, and a power supply system 30 (e.g., aswitched-mode power supply) for powering and controlling the brightnessof the light source 20 based on the signal from the input source 10.

The input source 10 may include an alternating current (AC) power sourcethat may operate at a voltage of 100 Vac, a 120 Vac, a 240 Vac, or 277Vac, for example. The input source 10 may also include a dimmerelectrically powered by said AC power sources. The dimmer may modify(e.g., cut/chop a portion of) the input AC signal according to a dimmerlevel before sending it to the power supply system 30, and thus variablyreduces the electrical power delivered to the power supply system 30 andthe light source 20. In some examples, the dimmer may be a TRIAC or ELVdimmer, and may chop the front end or leading edge of the AC inputsignal. According to some examples, the dimmer interface may be a rockerinterface, a tap interface, a slide interface, a rotary interface, orthe like. A user may adjust the dimmer level by, for example, adjustinga position of a dimmer lever or a rotation of a rotary dimmer knob, orthe like. The light source 20 may include one or morelight-emitting-diodes (LEDs) or an arc or gas discharge lamp withelectronic ballasts, such as high intensity discharge (HID) orfluorescent lights.

In some embodiments, the power supply system 30 includes a rectifier 40,a converter 50, and an output correction circuit (e.g., a secondary-sideoutput correction circuit) 100.

The rectifier 40 may provide a same polarity of output for eitherpolarity of the AC signal from the input source 10. In some examples,the rectifier 40 may be a full-wave circuit using a center-tappedtransformer, a full-wave bridge circuit with four diodes, a half-wavebridge circuit, or a multi-phase rectifier.

The converter (e.g., the DC-DC converter) 50 converts the rectified ACsignal generated by the rectifier 40 into a drive signal for poweringand controlling the brightness of the light source 20. The drive signalmay depend on the type of the one or more LEDs of the light source 20.For example, when the one or more LEDs of the light source 20 areconstant current LEDs the drive signal may be a variable voltage signal,and when the light source 20 requires constant voltage, the drive signalmay be a variable current signal. In some embodiments, the converter 50includes a boost converter for maintaining (or attempting to maintain) aconstant DC bus voltage on its output while drawing a current that is inphase with and at the same frequency as the line voltage (by virtue ofthe power factor correction (PFC) controller 60). Another switched-modeconverter (e.g., a transformer) inside the converter 50 produces thedesired output voltage from the DC bus. The converter has a primary side52 and a secondary side 54 that is electrically isolated from, andinductively coupled to, the primary side 52. In some examples, the PFCcontroller 60 may be configured to improve (e.g., increase) the powerfactor of the load on the input source 10 and reduce the total harmonicdistortions (THD) of the power supply system 30. The PFC controller 60may be external to the converter 50, as shown in FIG. 1, or may beinternal to the converter 50.

According to some embodiments, the output correction circuit 100monitors the output (e.g., the output voltage and current) of theconverter 50 on the secondary side and issues a correction signal thatis fed back into the primary side 52 of the power supply system 30. Thecorrection signal may be utilized by the PFC controller 60 to drive themain switch 56 within the converter 50, which determines the DC outputlevel of the power supply system 30.

The power supply system 30 may not be able to produce a perfect DCsignal at its output and ripples may be present in the output. Forexample, there may be an inherent sine wave ripple at the output signal,which originates from the line input voltage that is supplied to thepower supply system 30. The voltage ripples may affect the DC outputcurrent of the power supply system 30, and the peak-to-peak voltage ofthe ripples may vary significantly depending on load. For example, theoutput signal may exhibit a smaller peak-to-peak ripple at high voltageloads (e.g., when at high brightness settings or driving a high-voltageLED) and a relatively larger peak-to-peak ripple at low voltage loads(e.g., when at low driver settings or driving a low-voltage LED). In therelated art, this ripple may affect the operation of the feedback loopand lead to an error in the DC level of the output signal. That is, theDC level of the output signal may deviate from the desired output value(as, e.g., determined by a brightness setting). For example, when thedesired dimmer setting is at 50%, the ripple at the output of the powersupply system 30 may cause the output level to be at 49% and not thedesired 50%. This error may be particularly pronounced in single stagetopologies using a PFC, such as flyback topologies, pure buckconverters, or buck-boost converters.

According to some embodiments, the output correction circuit 100 correctfor this error to ensure that the DC level of the output signalaccurately represents the desired setting. In some embodiments, theoutput correction circuit 100 measures the ripple of the output voltageV_(OUT) of the converter 50, measures the output current (e.g.,instantaneous output current) I_(OUT) of the converter 50, adjusts areference signal that corresponds to the desired output based on theoutput voltage VOUT to compensate for the measured ripple, and comparesthe adjusted reference signal with the measured output current I_(OUT)to generate the correction signal. In some embodiments, the correctionsignal is used to dynamically control a DC-level of the output signal ofthe converter 50 based on the measured ripple and the reference signal,which corresponds to the desired DC-level of the output signal.

In some examples, an optocoupler 70 communicates the control signal fromthe output correction circuit 100 on the secondary side 54 to theprimary side 52, while maintaining the electrical isolation between thetwo sides.

FIG. 2 is a schematic diagram illustrating the output correction circuit100 within the power supply system 30, according to some exampleembodiments of the present disclosure.

According to some embodiments, the output correction circuit 100 iselectrically coupled to the secondary side 54 of the converter 50 andelectrically isolated from the primary side 52. The output correctioncircuit 100 includes sense resistor (R_(SENSE)) 102, a current sensecircuit 104, an operational amplifier (also referred to as an erroramplifier) 106, and a reference generator (e.g., a reference voltage orcurrent generator) 108. The sense resistor 102 may be positioned betweenan output terminal (e.g., a reference/ground terminal) of the converter50 and the light source 20 and is connected electrically in series withthe light source 20. In some examples, the sense resistor may be about50 mΩ to about1 Ω.

In some embodiments, the current sense circuit 104 measures the outputcurrent I_(OUT) of the converter 50 via the sense resistor 102, andprovides a sense signal (e.g., a sense voltage) V_(SENSE) correspondingto the measured output current I_(OUT) to the first input terminal(e.g., the negative terminal) of the error amplifier 106 to compare withan adjusted reference signal (e.g., an adjusted referencecurrent/voltage) V_(AREF) supplied by the reference generator 108. Insome examples, the sense signal V_(SENSE) is the voltage drop across thesense resistor 102. The correction signal (also referred to as acorrected control signal) V_(CORR) that is then generated by the erroramplifier 108 is used by the PFC controller 70 to control the main gate56 of the converter 50 (e.g., via a gate control signal V_(GATE)), whichin turn controls/adjusts the voltage level of the converter outputV_(out). In some examples, the optocoupler 70 transmits the correctionsignal V_(CORR) across the primary-secondary barrier to the PFCcontroller 70, while maintaining electrical isolation between theprimary and secondary sides 52 and 54.

According to some embodiments, the reference generator 108 includes aprocessor (e.g., a programmable microprocessor) 110, a memory (e.g., astorage memory) 112, an analog-to-digital (A/D) converter 114 at aninput terminal (e.g., a sample terminal) 115, and a digital-to-analog(D/A) converter 116 at an output terminal 117. The sample terminal ofthe reference generator 108 is electrically coupled the output of theconverter 50 and samples (e.g., measures) the output voltage V_(out) ofthe converter 50. The ND converter converts the readings to digitalbinary form for further processing by the processor 110.

In some embodiments, processor 110 calculates the voltage ripple (e.g.,the peak-to-peak voltage ripple) at the output of the converter 50 basedon the measurements captured by the ND converter 116 and uses it tomodify/adjust a reference signal that corresponds to the DC value thatoutput signal (e.g., output current or voltage) of the converter 50 isto be regulated to. The D/A converter 116 converts the adjustedreference signal, which may be in digital binary format, to an analogsignal to be supplied to the error amplifier 106 (e.g., to the positiveinput terminal of the error amplifier 106) via the output terminal 117.

The reference signal V_(REF) may be a fixed/constant value stored at thememory 112 or may be variable signal provided from an external circuit.In examples in which the light source 20 is a dimmable light (e.g., adimmable LED), a dimming controller 80 may generate the reference signalV_(REF) based on a dimmer setting (e.g., a brightness setting rangingfrom 0-100%) and provide the signal to the processor 110.

In the absence of any ripple in the output signal, providing thereference signal VREF to error amplifier 106 may result in the outputsignal (e.g., V_(OUT) or I_(OUT)) regulating to the desired valueassociated with the reference signal V_(REF). However, the presence ofripple at the output of the converter 50 may cause deviations in theoutput signal from the desired value. In some examples, the ripplepercentage (e.g., peak-to-peak ripple percentage) may be about 5% toabout 40% of the DC-level at the converter output.

According to some embodiments, by observing the output of the converter50, the output correction circuit 100 determines the peak-to-peakvoltage ripple (V_(PP)) and the actual DC voltage level of output signal(V_(OUT)(DC)) in real-time, and calculates the percentage ripple (%ripple) as

% ripple=V _(PP) /V _(OUT)(DC) * 100%.   (Eq. 1)

In some embodiments, the output correction circuit 100 thencorrects/adjusts the reference signal (V_(REF)) based on the percentageripple (e.g., a real-time percentage ripple) using a look-up table (LUT)or a formula. According to some embodiments, the LUT or formulacorrelate various percentage ripples at the output of the power supplysystem 30 to different scaling/correction factors for compensating thereference signal. The formula may express correction factor as afunction of percentage ripples.

Once the correction factor (CF) is determined, the output correctioncircuit 100 calculates the adjusted reference signal (V_(AREF)) as

V _(AREF)=CF *V_(REF)   (Eq. 2)

By compensating for the effect of ripple on the feedback loop, theadjusted reference signal may lead to an output signal (e.g., an outputcurrent I_(OUT) and/or an output voltage V_(OUT)) whose DC level moreclosely matches the desired output DC level (as, e.g., determined by thedimmer setting) than the original reference signal.

As the output capacitance C_(OUT) of the converter 50 may have an effecton the output ripple, in some embodiments, the processor 110 usesdifferent LUTs or formulas for different output capacitance C_(OUT)values. As the LUT(s) or formula(s) utilize percent ripple, as opposedto absolute ripple values, the correction factors are not dependent on(e.g., not a function of) the DC level of the output signal. That is,the correction factor for a given ripple percentage is equallyapplicable to output signals having different DC levels. For example,the same LUT or formula may be used for different dimmer settings anddifferent LEDs. The LUT(s) and formula(s) may be stored at the memory112 for fast retrieval by the processor 110.

Table 1 below illustrates examples of LUTs for three different outputcapacitance values, according to some example embodiments of the presentdisclosure.

TABLE 1 Cout = 2700 μF Cout = 2200 μF Cout = 1500 μF Vout % CorrectionVout % Correction Vout % Correction (v) Ripple Factor (CF) (v) RippleFactor (CF) (v) Ripple Factor (CF) [0, 10) 0 0.9918 [0, 10) 0 0.9976 [0,10) 0 1.0000 [10, 19) 3.94 0.9918 [10, 11) 4.51 0.9976 [10, 11) 6.021.0000 7.18 1.0000 8.54 1.0153 [11, 19) 1.08 1.0382 9.42 1.0321 [11, 19)2.70 1.0571 2.68 1.0610 [19, 20) 0.00 1.0321 [19, 20) 0.00 1.0571 4.521.0714 [20, 29) 0.00 0.9883 [20, 29) 0.00 0.9860 6.78 1.0857 2.16 0.98832.57 0.9860 [19, 20) 0.00 1.0857 4.04 0.9923 5.49 1.0076 [20, 29) 0.000.9918 5.23 1.0030 7.28 1.0264 3.40 0.9918 5.99 1.0085 [29, 30) 0.001.0264 7.36 1.0397 [29, 30) 0.00 1.0085 [30, 39) 0.00 0.9800 9.87 1.0500[30, 39) 0.00 0.9849 1.88 0.9800 [29, 30) 0.00 1.0500 1.48 0.9849 3.621.0100 [30, 39) 0.00 0.9918 2.66 0.9902 4.76 1.0178 2.49 0.9918 3.041.0100 5.48 1.0264 4.87 1.0150 3.39 0.9950 [39, 40) 0.00 1.0464 5.461.0300 4.00 1.0107 [40, 49) 0.00 0.9837 7.17 1.0450 4.41 1.0107 1.280.9837 [39, 40) 0.00 1.0450 5.00 1.0300 1.34 0.9800 [40, 49) 0.00 0.9860[39, 40) 0.00 1.0500 1.46 0.9750 1.91 0.9860 [40, 100) 0.00 0.9825 2.720.9897 3.05 0.9964 1.19 0.9825 3.08 0.9938 5.49 1.0110 2.56 0.9877 [49,50) 0.00 0.9938 5.60 1.0300 3.24 0.9908 [50, 100) 0.00 0.9864 [49, 50)0.00 1.0110 >=100 0.00 1.0000 1.82 0.9864 [50, 100) 0.00 0.9856 2.460.9898 1.73 0.9856 >=100 0.00 0.9898 3.33 1.0100 >=100 0.00 1.0100

As shown in Table 1, in some embodiments, the LUT includes, for eachoutput voltage range, ordered pairs of percentage ripples and associatedcorrection factors. In some examples, the correction factors tabulatedin the LUT(s) may be determined experimentally as values needed toachieve a desired DC level for the output signal given differentpercentage ripple values.

As will be understood by a person of ordinary skill in the art, thevalues and ranges provided in Table 1 are only provided as an example,and may be changes to any other suitable values and ranges depending onthe application.

In some embodiments, when a calculated percentage ripple matches one ofthe values in the LUT, the processor 110 uses the correspondingcorrection factor to adjust the reference signal. When, within aparticular output voltage range, a percentage ripple value falls betweena first percentage value and a second percentage value from the LUT, theprocessor 110 calculates the correction factor CF by performinginterpolation (e.g., linear interpolation) between first and secondcorrection factors corresponding to the first and second percentagevalues. In some examples, the interpolation operation performed by theprocessor 110 may be expressed in code as:

 if (input <= inputPoint[0]) // inputPoint[0] being a first tabulated %ripple   result = outputPoint[0]; // outputPoint[0] being a firsttabulated CF  else if (input >= inputPoint[numPoints−1]) // numPoints =No. of tabulated % ripple values   result = outputPoint[numPoints−1]; else  {   // Bracket the steps, find where point lies within the inputrange   for (i=0; i<(numPoints−1); i++)    if ((input > inputPoint[i])&& (input <= inputPoint[i+1]))     range = i;   // Calculate thestep-delta between the two points   if ((inputPoint[range+1] −inputPoint[range]) != 0) // catch /0    delta = (outputPoint[range+1] −outputPoint[range]) * 100 / (inputPoint[range+1] − inputPoint[range]);  else    delta = 1.0;   // Add or subtract the scaled location * delta,to the lower point   result = outputPoint[range] + (delta * (input −inputPoint[range])) / 100;  }

Accordingly, as described above, the power supply system 30 utilizes theoutput correction circuit 100 to compensate for the deviation caused inthe DC-level of the output signal of the power supply system by theripple present in the output signal. In some embodiments, the outputcorrection circuit 100 monitors the peak-to-peak ripple in the outputsignal of the power supply system and provides an adjusted referencesignal to the error amplifier to compensate for the effect of theobserved ripple on the DC-level of the output signal. This allows thepower supply system to deliver a more accurate and precise current levelto the load.

It will be understood that, although the terms “first”, “second”,“third”, etc., may be used herein to describe various elements,components, regions, layers, and/or sections, these elements,components, regions, layers, and/or sections should not be limited bythese terms. These terms are used to distinguish one element, component,region, layer, or section from another element, component, region,layer, or section. Thus, a first element, component, region, layer, orsection discussed below could be termed a second element, component,region, layer, or section, without departing from the spirit and scopeof the inventive concept.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting of the inventive concept.As used herein, the singular forms “a” and “an” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “include”,“including”, “comprises”, and/or “comprising”, when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof. As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items. Further, the use of “may” when describingembodiments of the inventive concept refers to “one or more embodimentsof the inventive concept”. Also, the term “exemplary” is intended torefer to an example or illustration.

As used herein, the terms “use”, “using”, and “used” may be consideredsynonymous with the terms “utilize”, “utilizing”, and “utilized”,respectively.

The power supply system with the output correction circuit and/or anyother relevant devices or components according to embodiments of thepresent invention described herein may be implemented by utilizing anysuitable hardware, firmware (e.g., an application-specific integratedcircuit), software, or a suitable combination of software, firmware, andhardware. For example, the various components of the independentmulti-source display device may be formed on one integrated circuit (IC)chip or on separate IC chips. Further, the various components of the LEDdriver may be implemented on a flexible printed circuit film, a tapecarrier package (TCP), a printed circuit board (PCB), or formed on thesame substrate. Further, the various components of the LED driver may bea process or thread, running on one or more processors, in one or morecomputing devices, executing computer program instructions andinteracting with other system components for performing the variousfunctionalities described herein. The computer program instructions arestored in a memory which may be implemented in a computing device usinga standard memory device, such as, for example, a random access memory(RAM). The computer program instructions may also be stored in othernon-transitory computer-readable media such as, for example, a CD-ROM,flash drive, or the like. Also, a person of skill in the art shouldrecognize that the functionality of various computing devices may becombined or integrated into a single computing device, or thefunctionality of a particular computing device may be distributed acrossone or more other computing devices without departing from the scope ofthe exemplary embodiments of the present invention.

While this invention has been described in detail with particularreferences to illustrative embodiments thereof, the embodimentsdescribed herein are not intended to be exhaustive or to limit the scopeof the invention to the exact forms disclosed. Persons skilled in theart and technology to which this invention pertains will appreciate thatalterations and changes in the described structures and methods ofassembly and operation can be practiced without meaningfully departingfrom the principles, spirit, and scope of this invention, as set forthin the following claims and equivalents thereof.

What is claimed is:
 1. A power supply system comprising: a converterconfigured to generate an output signal based on a rectified inputsignal for driving a light source; and an output correction circuitcoupled to an output of the converter and configured to measure a ripplein the output signal and to generate a correction signal to dynamicallycontrol a DC-level of the output signal of the converter based on themeasured ripple and a reference signal corresponding to a desiredDC-level of the output signal.
 2. The power supply system of claim 1,wherein the output signal is an output current or an output voltage ofthe converter, and wherein the converter is a DC-DC converter.
 3. Thepower supply system of claim 1, wherein the output correction circuitcomprises: a sense resistor electrically coupled between an outputterminal of the converter and the light source driven by the converter;and a current sense circuit coupled to the sense resistor and configuredto measure an output current of the converter via the sense resistor,and to generate a sense signal corresponding to the measured outputcurrent.
 4. The power supply system of claim 1, wherein the outputcorrection circuit comprises: a sense resistor configured to sense anoutput current of the converter; a reference generator configured togenerate an adjusted reference signal; and an operational amplifierconfigured to receive the adjusted reference signal and a sense signalcorresponding to the sensed output current, and to generate thecorrection signal based on a difference between the adjusted referencesignal and the sensed output current.
 5. The power supply system ofclaim 4, wherein the reference generator is configured to monitor anoutput voltage of the converter, to determine a percentage ripple in theoutput signal based on the monitored output voltage, and to adjust thereference signal based on the percentage ripple.
 6. The power supplysystem of claim 5, wherein the reference generator is further configuredto measure a peak-to-peak voltage ripple in the output voltage and aDC-level of the output voltage, and to calculate the percentage ripplebased on the peak-to-peak voltage ripple and the DC-level of the outputvoltage.
 7. The power supply system of claim 5, wherein the referencegenerator is further configured to calculate a correction factor basedon the calculated percentage ripple and a look-up table (LUT) comprisingordered pairs of percentage ripples and associated correction factors.8. The power supply system of claim 7, wherein the reference generatoris further configured to calculate the correction factor byinterpolating between two adjacent correction factors stored in the LUT.9. The power supply system of claim 7, wherein the reference generatoris further configured to calculate the adjusted reference signal bymultiplying the reference signal by the correction factor.
 10. The powersupply system of claim 5, wherein the reference generator is furtherconfigured to calculate a correction factor based on the calculatedpercentage ripple and a formula that relates correction factors topercentage ripples.
 11. The power supply system of claim 5, wherein thereference generator comprises: a memory configured to store a look-uptable (LUT) comprising ordered pairs of percentage ripples andassociated correction factors; and a processor configured to calculate acorrection factor based on and the LUT comprising ordered pairs ofpercentage ripples and associated correction factors, and to calculatethe adjusted reference signal based on the reference signal and thecorrection factor.
 12. The power supply system of claim 11, wherein thememory is configured to store a plurality of LUTs corresponding todifferent values of an output capacitance of the power supply system.13. The power supply system of claim 5, wherein the reference generatoris configured to receive the reference signal from a dimming controller,the reference signal being based on a dimmer setting.
 14. The powersupply system of claim 1, wherein the output correction circuit iselectrically isolated from a primary side of the converter.
 15. Thepower supply system of claim 1, further comprising: a rectifierconfigured to rectify an input signal to generate the rectified inputsignal having a single polarity.
 16. The power supply system of claim 1,wherein the output correction circuit is configured to provide thecorrection signal to the converter, and wherein the converter isconfigured to regulate a DC-level voltage of the output signal based onthe correction signal.
 17. The power supply system of claim 1, furthercomprising: a power factor correction (PFC) controller coupled to aprimary side of the converter, wherein the output correction circuit isconfigured to provide the correction signal to the PFC controller, andwherein the PFC controller is configured to regulate a DC-level voltageof the output signal based on the correction signal.
 18. The powersupply system of claim 1, wherein the converter has a primary side and asecondary side electrically isolated from, and inductively coupled to,the primary side.
 19. The power supply system of claim 13, wherein theoutput correction circuit is configured to communicate the correctionsignal to a primary side of the converter via an optocoupler.